This invention relates generally to streaming media objects and, more particularly, to broadcast schemes for streaming media objects on demand from a server to a client over a digital network.
Media-on-Demand (MoD), and in particular Video-on-Demand (VOD), is becoming a popular digital network application. One highly scalable scheme known for facilitating MoD) and VoD, and reducing the cost of MoD and VoD especially for popular media objects, is called periodic broadcast. In this scheme, media objects are broadcast periodically, and multiple users are served via one single transmission, thus substantially reducing the bandwidth requirements for the most frequently requested media objects. Most current periodic broadcast schemes assume Constant-Bit-Rate (CBR) encoded media objects rather than Variable-Bit-Rate (VBR) encoded media objects. This is despite the fact that, for the same video and the same desired image quality, CBR encoding requires twice or more bandwidth than that required for VBR encoding. However, the few existing proposals that support the bandwidth-efficient family of VBR encoded media objects suffer from data loss because they allow the aggregate traffic of the simultaneously-transmitted segments of the media contents to exceed the broadcast link capacity. Accordingly, there are no existing schemes that can provide lossless delivery of media content while guaranteeing a minimum latency and quality of service, while also allowing bandwidth requirements on both the sending and receiving ends to be easily designed.
The present invention relates to a method and apparatus for broadcasting media objects for such bandwidth-intensive applications as Media on Demand (MoD) or Video on Demand (VoD) in accordance with a novel StairCase Broadcast (SCB) scheme. A media server in accordance with one example of the invention includes a fragmenter that fragments media objects into multiple segments, with each segment provided to a corresponding streamer. Each streamer periodically and continuously streams data associated with its corresponding media segment on a connection between the server and a media client. A download controller in the media client selectively causes the proper streams to be received for downloading from the server in accordance with the fragmentation of the selected media object and the number of streams that the client can simultaneously receive for downloading. A selector is operable to cause data from each successive segment to be downloaded from the corresponding stream immediately regardless of the position in the period associated with the successive segment. By its design, the method and apparatus of the present invention allow for lossless broadcast of media contents with de-coupled per-media-object server and client bandwidth design considerations.
In accordance with one aspect of the invention, a method for providing a media object to a client from a server coupled to the client via a connection, the media object being fragmented into segments in accordance with a fragmentation sequence from a first segment to a last segment, each segment comprising a respective number of frames of media content in a respective succession from a first frame to a last frame, comprises the steps of causing the media content associated with each of the segments to be provided on a corresponding stream in accordance with the succession from the first frame to the last frame, providing a first number of the streams on the connection, the first number of the streams including the corresponding stream to the first segment, halting the provision of the corresponding stream to the first segment on the connection when the respective number of frames of the first segment have been provided on the corresponding stream, providing a next stream corresponding to a next segment in the fragmentation sequence on the connection after the halting step, and starting the step of providing the next stream at a point in the respective succession between the first frame and the last frame.
In accordance with a further aspect of the invention, an apparatus for providing a media object to a client from a server coupled to the client via a connection, the media object being fragmented into segments in accordance with a fragmentation sequence from a first segment to a last segment, each segment comprising a respective number of frames of media content in a respective succession from a first frame to a last frame, the apparatus comprises means for causing the media content associated with each of the segments to be provided on a corresponding stream in accordance with the succession from the first frame to the last frame, means for providing a first number of the streams on the connection, the first number of the streams including the corresponding stream to the first segment, means for halting the provision of the corresponding stream to the first segment on the connection when the respective number of frames of the first segment have been provided on the corresponding stream, means for providing a next stream corresponding to a next segment in the fragmentation sequence on the connection after the halting step, and means for starting the step of providing the next stream at a point in the respective succession between the first frame and the last frame.
In accordance with a further aspect of the invention, a method of fragmenting a media object into a fragmentation comprising a plurality Km of segments, the segments having a sequence from a first segment to a last segment, the media object having a plurality Nm of frames of media data, the method comprises the steps of initializing the fragmentation to Km=Nm segments, each segment containing one frame, determining, for each of the Km segments, a corresponding bandwidth required to download the segment, combining two successive segments in the sequence into a new segment, and: controlling the combining step so as to minimize a total variance between the corresponding bandwidth for each of the Km segments.